In a statement the Metropolitan Police said a 51-year-old Detective Constable had been arrested at work on Thursday afternoon on suspicion of leaking information.

Deputy Assistant Commissioner Sue Akers, in charge of Operation Weeting, said: "I made it very clear when I took on this investigation the need for operational and information security. It is hugely disappointing that this may not have been adhered to.

"The MPS takes the un-authorised disclosure of information extremely seriously and has acted swiftly in making these arrests."

Police also announced they had arrested and bailed former News of the World feature writer, 35-year-old Dan Evans, on suspicion of phone hacking on Friday, saying: "He was arrested by appointment at a London police station at 10.30 this morning and subsequently bailed to return on a date in October."

Evans had been suspended from the paper.

A News International spokesperson said: "We are fully co-operating with the police investigation and we are unable to comment further on matters due to ongoing police investigations."

A spokesperson for the paper's publisher Guardian News & Media said: "We note the arrest of a Scotland Yard detective on suspicion of misconduct in a public office relating to unauthorised disclosure of information.

"On the broader point raised by the arrest, journalists would no doubt be concerned if conversations between off-the-record sources and reporters came routinely to be regarded as criminal activity. In common with all news organisations we have no comment to make on the sources of our journalism."